The present invention relates generally to anti-skid control employed for braking of a motor vehicle, and more particularly to an anti-skid control system for optimally controlling a braking hydraulic pressure to each of wheel braking cylinders to prevent the wheels from being locked on braking operation.
Various anti-skid control systems have hitherto been developed with a view to preventing their wheels from falling into a locked condition, i.e., skid condition in excess of a limit of frictional force between the tire and a road surface as a result of a quick braking action of the vehicle.
U.S. Pat. No. 3,637,264 or U.S. Pat. No. 4,054,328, for example, discloses an anti-skid control system wherein a braking pressure to each of wheels is controlled on the basis of parameters derived as a function of a wheel speed so that a slip ratio of the wheel becomes equal to a target slip ratio. However, these prior art systems are arranged to adjust a braking pressure applied to each of the wheels each time in response to variations of road surface conditions and so on, and therefore the variations of wheel speed cover a wide range irrespective of the fact that the vehicle speed has been reduced by a braking operation, resulting in unstable braking control. Furthermore, according to the prior art arrangement, it is required to establish many control conditions in advance to effectively perform the anti-skid control in any vehicle running conditions, resulting in a complex control system.